The present invention relates to a photoelectric converter, such as an LED head or image sensor, and more particularly to a photoelectric converter which requires a plurality of printed wiring boards in a light emitting section of an LED head or in a light receiving section of an image sensor and comprises a linear array of photoelectric conversion devices such as LED chips or photodiodes at uniform intervals or spacing.
A light emitting section of a conventional LED head comprises a linear array of LED chips 12 on a printed wiring board 11 as shown in FIG. 1 and a plurality of LED chip drive ICs (not shown) along the LED chip array. A light receiving section of an image sensor comprises a linear array of sensor chips such as photodiode chips at even pitches on a printed wiring board (not shown) like the LED chips 12 of the LED head.
To enlarge a photoelectric converter comprising the light emitting section of the LED head, the light receiving section of the image sensor, etc., if the printed wiring board is made a single longer board, productivity lowers; even if the printed wiring board is made longer, an appropriate circuit wiring pattern must be formed for each length of the printed wiring boards formed to have desired lengths, that is, different kinds of circuit wiring patterns are required, thus it becomes difficult to standardize them, increasing costs drastically. Therefore, previously, for example, the LED head was made longer by butting together the printed wiring boards 11 with LED chips 12 and 12' arranged as shown in FIG. 2. At the time, to prevent uneven print from occurring in the butted part, each LED chip 12' on the butt end of each printed wiring board 11 was mounted so as to project from the end of the printed wiring board 11 and the LED chips 12 and 12' were arranged at equal intervals as much as possible for making the intervals of light emitting points equal pitches.
To provide a longer LED head, for example, as described in Japanese Utility Model Unexamined Publication No. Hei 2-127442, a method is proposed wherein a plurality of printed wiring boards are butted together without any gap and an LED chip 12 is disposed across the butted part, as shown in FIG. 3, for placing light emitting points at equal pitches.
However, to project LED chips from the ends of the printed wiring boards and arrange light emitting points at uniform pitches as shown in FIG. 2, alignment on the order of tens of .mu.m must be made, thus it is hard to work and takes a long time and additional jigs and accessories for aligning the light emitting points are further required. If the printed wiring board on which LED chips are mounted expands or contracts due to a temperature change (temperature cycle) at operation or in an operating environment, the distance between the LED chips at the butted part on the ends of the printed wiring boards changes and the pitch between the light emitting points becomes uneven, causing uneven print, etc., to occur, thereby lowering product reliability.
Further, when the printed wiring boards are butted together without any gap and an LED chip is disposed across the butted part as shown in FIG. 3, since LED chips are mounted on the printed wiring board, expansion or contraction of the printed wiring board due to a temperature cycle causes the spaces between the LED chip mounted across the butted part and its adjacent LED chips to change. Further, if the respective printed wiring boards contain a thickness error and the adjacent printed wiring boards differ from each other in thickness, the LED chips arranged for each of the printed wiring boards differ in height and emitted light is placed out of focus. Also, the LED chip mounted across the butted part inclines due to a step difference occurring at the butted part, placing emitted light out of focus. Further, the LED chip may be broken.